The human brain is an exceedingly delicate structure protected by a series of envelopes to protect it from injury. The innermost layer, the pia mater, covers the surface of the brain. The arachnoid layer, adjacent to the pia mater, is a spidery web-like membrane that acts like a waterproof membrane. Finally, the dura mater, a tough leather-like layer, covers the arachnoid layer and adheres to the bones of the skull.
While this structure protects against penetrating trauma, the softer inner layers absorb only a small amount of energy before linear forces applied to the head are transmitted to the brain. When an object strikes a human head, both the object and the human head are moving independently and often in different angles thus, angular forces, as well as linear forces, are almost always involved in head injuries. Many surgeons in the field believe the angular or rotational forces applied to the brain are more hazardous than direct linear forces due to the twisting or shear forces they apply to the white matter tracts and the brain stem.
One type of brain injury that occurs frequently is the mild traumatic brain injury (MTBI), more commonly known as a concussion. Such injury occurs in many settings, such as, construction worksites, manufacturing sites, and athletic endeavors and is particularly problematic in contact sports. While at one time a concussion was viewed as a trivial and reversible brain injury, it has become apparent that repetitive concussions, even without loss of consciousness, are serious deleterious events that contribute to debilitating irreversible diseases, such as dementia and neuro-degenerative diseases including Parkinson's disease, chronic traumatic encephalopathy (CTE), and dementia pugilistica.
U.S. Pat. No. 5,815,846 (Calonge) describes a helmet with fluid filled chambers that dissipate force by squeezing fluid into adjacent equalization pockets when external force is applied. In such a scenario, energy is dissipated only through viscous friction as fluid is restrictively transferred from one pocket to another. Energy dissipation in this scenario is inversely proportional to the size of the hole between the full pocket and the empty pocket. That is to say, the smaller the hole, the greater the energy drop. The problem with this design is that, as the size of the hole is decreased and the energy dissipation increases, the time to dissipate the energy also increases. Because fluid filled chambers react hydraulically, energy transfer is in essence instantaneous. Hence, in the Calonge design, substantial energy is transferred to the brain before viscous fluid can be displaced negating a large portion of the protective function provided by the fluid filled chambers. Viscous friction is too slow an energy dissipating modification to adequately mitigate concussive force. If one were to displace water from a squeeze bottle one can get an idea as to the function of time and force required to displace any fluid when the size of the exit hole is varied. The smaller the transit hole, the greater the force required and the longer the time required for any given force to displace fluid.
U.S. Pat. No. 3,872,511 (Nichols) describes a helmet with hard inner and outer shells with an intermediate zone between the two shells. The zone contains a plurality of fluid-filled bladders that are held to the inner surface of the outer shell by means of a valve. When an impact occurs the outer shell is forced into the zone, squeezing the bladders. The valve closes upon impact causing the air to be retained in the bladders to cushion the impact from the user's head. However, because the movement of the bladders is restricted at impact, the force of the impact, although reduced is still directed into the head. In addition, the Nichols patent makes no provision for mitigation of rotational forces striking the helmet.
U.S. Pat. No. 6,658,671 (Hoist) describes a helmet with inner and outer shells and a sliding layer. The sliding layer allows for the displacement of the outer shell relative to the inner shell to help dissipate some of the angular force during a collision applied to the helmet. However, the force dissipation is confined to the outer shell of the helmet. In addition, the Holst helmet provides no mechanism for returning the two shells to the resting position relative to each other. A similar shortcoming is shown in the helmets described in U.S. Pat. No. 5,956,777 (Popovich) and European patent publication EP 0048442 (Kalman et al.).
German Patent DE 19544375 (Zhan) describes a construction helmet that includes apertures in the hard outer shell that allows the expansion of cushion material through the apertures to dispel some of the force of a collision. However, because the inner liner rests against a user's head, some force is directed toward rather than away from the head.
U.S. Patent Application Publication No. 2012/0198604 (Weber et al.) describes a safety helmet for protecting the human head against repetitive impacts as well as moderate and severe impacts to reduce the likelihood of brain injury caused by both translational and rotational forces. The helmet includes isolation dampers that act to separate an outer liner from an inner liner. Gaps are provided between the ends of the outer liner and the inner liner to provide space to enable the outer liner to move without contacting the inner liner upon impact.
Clearly, to prevent traumatic brain injury, not only must penetrating objects be stopped, but any force, angular or linear, imparted to the exterior of the helmet must also be prevented from simply being transmitted to the enclosed skull and brain. The helmet must not merely play a passive role in dampening such external forces, but must play an active role in dissipating both linear and angular momentum imparted such that they have little or no deleterious effect on the delicate brain.
To afford maximum protection from linear and angular forces, the outer shell of a helmet mitigating such force must be capable of movement independent from the inner shell of the helmet which covers and encloses the skull and brain, such that any force vector or vectors can be allayed prior to the force getting to the brain.
To attain these objectives in a helmet design, the inner component (shell) and the outer component (shell or shells) must be capable of appreciable degrees of movement independent of each other. Additionally, the momentum imparted to the outer shell should both be directed away from and/or around the underlying inner shell and brain and sufficiently dissipated or stored so as to negate deleterious effects.
Thus, there is a long-felt need for a protective helmet having an energy storage mechanism that absorbs linear and rotational forces and slowly releases such forces.